Microstructural Evolution and Material Flow during Friction Stir Welding of 6013 Aluminum Alloy Studied by the Stop-Action Technique

Abstract

This work is part of a wide-ranging study aiming to enhance the technology of dissimilar friction-stir welding of aluminum and titanium. In the previous study, a new approach was proposed that provided an exceptionally narrow intermetallic layer. However, an essential disadvantage of this technique was the significant material softening in the aluminum part. Hence, the present work was undertaken in order to obtain insight into microstructural processes and material flow in the aluminum part. To this end, the stop-action technique was applied. It was found that the microstructural evolution included several stages. Specifically, the initial material underwent the discontinuous static recrystallization in the heat-affected zone. With the approach of the rotating tool, the recrystallized grains experienced continuous dynamic recrystallization, which resulted in grain refinement. The subsequent transportation of material around the rotating tool provided no significant alterations in microstructure. This “superplastic-like” character of material flow was attributed to a dynamic balance between grain refinement and grain coarsening. It was also found that the stirred material experienced a secondary deformation induced by the rotating tool shoulder far behind the welding tool. The concomitant microstructural changes were most pronounced at the upper weld surface and gave rise to a fine-grained layer.

The Regularities of Metal Transfer by a Nickel-Based Superalloy Tool during Friction Stir Processing of a Titanium Alloy Produced by Wire-Feed Electron Beam Additive Manufacturing

“…However, in the case of titanium alloys, the process of the stir zone formation by FSW/P and the peculiarities of material flow are still underexplored. The stop-action technique [18] is the most suitable for studying the deformation peculiarities and the material structure formation in the FSW-tool effect zone. It allows us to simultaneously study both the structure of the workpiece and the features of tool wear during FSW/FSP and has found application even in the field of steel welding [19].…”

Regularities of Metal Transfer by Nickel-Based Superalloy Tool at Friction Stir Processing of Titanium Alloy, Produced by Wire Feed Electron Beam Additive Manufacturing

“…The stop-action technique [18] is the most suitable for studying the deformation peculiarities and the material structure formation in the FSW-tool effect zone. It allows to simultaneously study both the structure of the workpiece and the features of tool wear during FSW/P and has found its application even in the field of steel welding [19].…”